The present invention relates to the fabrication of large precision machined metal parts, and more particularly, to a method and apparatus for fabricating large copper segments of a helical coil which wraps around the toroidal conducting shell of a fusion reactor.
For many years there has been a worldwide effort toward the goal of harnessing fusion power as an inexhaustible source of energy for mankind. The basic fuel for atomic fusion is deuterium, an isotope of hydrogen that is easily and cheaply extracted from ordinary water. It is contemplated that deuterium extracted from sea water can supply human energy needs for billions of years at present rates of consumption. Atomic fusion is particularly desirable because it will have minimal environmental impact when compared with atomic fission. Although some radioactivity is generaged by the fusion process, the quantities and biological hazards are far less than those from other power sources, and in particular from atomic fission. In addition, problems of runaway, over-heating, or melt down reaction are virtually impossible in connection with atomic fusion.
Recently, Dr. Tihiro Ohkawa and his associates at General Atomic Company of San Diego, California, United States of America, have been developing a new magnetic fusion concept called Ohmic Heating Toroidal Experiment (OHTE). They have designed and constructed a prototype of a pilot fusion reactor to assess the physics and feasibility of a new plasma confinement concept.
The aforementioned OHTE reactor combines features from several other magnetic plasma confinement devices. It incorporates a large toroidal conducting shell like that utilized in reversed-field pinch systems. It also utilizes helical coils (H coils) similar to stellarator or torsatron windings. In addition, it incorporates an ohmic heating coil (E coil), vertical field coil (VF coil), and a plasma chamber similar to those of tokamak device.
In the OHTE reactor, the core is disposable in order to circumvent many material development problems for the first wall of the reactor. The device ignites with ohmic heating only. This obviates the need for the development of neutral beam or radio-frequency heating equipment. Since it does not require extremely high strength magnetic fields, the OHTE reactor does not utilize superconducting magnets.
The helical coil of the OHTE reactor must accommodate extremely high electric current levels. Therefore, it cannot be constructed by wrapping conventional copper cable around the toroidal conducting shell. This is because the magnetic fields surrounding the individual cables would tend to push the cables apart, thereby generating unacceptable mechanical stresses. Furthermore, conventional cable cannot be used for constructing the helical coil since the disposable core could not be readily removed and replaced.
The accurate placement of the center of the helical coil current relative to the plasma is an essential design requirement for the OHTE reactor. This requires close tolerance machining of the individual conductor segments of the helical coil, accurate location of the conductor segments on the toroidal conducting shell, and limited structural deflections of the helical coil during operation of the fusion reactor. Accordingly, the helical coil conductor segments must be fabricated from large pieces of hard copper. In addition, close tolerance machining of inside, outside and edge surfaces of the conductor segments is required. Close tolerance machining of conductor segment joint surfaces, ends, and bolt holes is also required.
Locating pins on the outer surface of the toroidal conducting shell are utilized to accurately locate each one of the conductor segments which make up the helical coil. Preferably, during operation of the fusion reactor, minimum deflection of the helical coil, for example less than one millimeter, occurs.
I have developed a novel method and apparatus for performing the close tolerance machining on the individual conductor segments which make up the helical coil of the OHTE fusion reactor.